Method of manufacturing a thermoplastic resin composition and moulded articles

ABSTRACT

Manufacturing a thermoplastic composition, there is first melt-blended a polymer (A)containing polyether chains, e.g. a polyetherpolyamide block copolymer, with (C) a vinyl compound, e.g. a copolymer of styrene and maleic anhydride and/or a compatibilizing agent (D), e.g. a graft copolymer with a polyolefin with an unsaturated carboxylic acid and the resultant melt-blended mixture is pelletized. The resultant pellets are then blended with a polyolefin (B) e.g. polyethylene. The resultant overall blended mixture can then be molded into films having a low variation in thickness of a desired permeability of water vapor and other gases.

INDUSTRIAL FIELD OF APPLICATION

The present invention relates to a method of producing a thermoplasticresin composition, and to moulded articles thereof. Its objective liesin offering a method of manufacturing a resin composition havingoutstanding extrusion moulding properties, and the water vapourpermeability of which can be controlled over a broad range whilemaintaining uniform performance, transparency, antistaticity and highgas permeability; together with moulded articles or packaging materialsformed therefrom.

PRIOR-ART

Hitherto, on account of their ease of handling and balanced properties,thermoplastic resins such as polyolefins have been widely used inapplications of various kinds, and they are also useful as packagingmaterials. In such circumstances, various materials have been devisedand employed according to the particular objectives, ranging frompermeable films of high gas permeability to barrier materials of lowpermeability, depending on the particular material, but few are endowedwith high water vapour permeability. For example, techniques are knownfor blending or laminating a material of high permeability and amaterial of low permeability. However, when used for the storage offoodstuffs, problems have arisen such as the condensing of the watervapour in the interior to form adhering water droplets so that thecontents are difficult to see, or the condensed moisture hastens thedeterioration of the contents and rotting readily occurs. Again, incases where longer term storage has been tried, there have been limitsto the control of the gas permeability.

In order to resolve such difficulties, there is known the introductionof fine pores into the film either mechanically by means of a needle orthe like or physico-chemically with a laser or the like, with thepermeability being controlled by the hole diameter and the density ofthe holes present (see, for example, Japanese Unexamined PatentPublication Nos 47-23478, 62-148247 and 2-85181, etc). Again, there hasbeen proposed the raising of the water vapour permeability by locallygreatly thinning the film without introducing holes. However, with thesemethods there is a great difference in the permeability between the poreregions and the other regions, and not only is it difficult to obtainuniformity over the entire film but there is also the disadvantage thatthe film strength is lowered and the selectivity of the gas permeabilityis reduced.

Now, methods have also been proposed which abandon the concept ofraising the permeability of the film itself and where, instead, a gas issealed inside which controls the metabolic action, or where there isintroduced an adsorbent for the harmful gases and moisture (see, forexample, Japanese Unexamined Patent Publication No. 3-14480, etc).However, as well as being time-consuming, the effects of these methodsare not altogether adequate.

On the other hand, compositions comprising a polyether-containing blockpolyamide or the like, along with a polyolefin and/or a functionalpolyolefin are known (see, for example, Japanese Unexamined PatentPublication No. 1-163234, and European Patent Nos 459862, 475963,559284, 657502 and 675167, etc). As the effects thereof, moisturepermeability, high impact properties and anti-static properties, etc,are described. However, these compositions comprisingpolyether-containing block polyamides and polyolefins have poormouldability even when a compatibilizing agent is incorporated, andarticles of stable product quality are hard to obtain.

PROBLEM TO BE RESOLVED BY THE INVENTION

As a result of intensive investigation aimed at controlling the watervapour permeability within a desired range with good reproducibility,while retaining high gas permeability and, moreover obtaining uniformperformance, such as transparency or antistaticity, the presentinventors discovered that these objectives could be attained byemploying the so-called master batch method in which a highconcentration of reactive compound is first blended, and then dilutionand reaction effected in stepwise fashion. It is on this discovery thatthe present invention is based.

MEANS FOR RESOLVING THE PROBLEM

The present invention is a method of manufacturing a thermoplastic resincomposition which is characterized in that, when blending a polymer (A)containing polyether chains as structural units and a polyolefin (B),the polymer (A) containing polyether chains as structural units is firstmelt-blended with a copolymer (C) of a vinyl compound and an unsaturateddicarboxylic acid or derivative thereof and/or a compatibilizing agent(D), after which the polyolefin (B) is then blended; together withmoulded articles and packaging materials obtained by this method.

It is clear that the polymer (A) is first melt blended with (C) only orwith (D) only or with (C) and (D).

In the present invention, ‘polymer (A) containing polyether chains asstructural units’ refers to block copolymer in which polyoxyalkylenechains and other polymer chains are linked together or to a polymer inwhich polyoxyalkylene chains are combined together via coupling regions.Here as examples of the polyoxy-alkylene, there can be citedpolyoxyethylene, poly(1,2- and 1,3-oxypropylene), polyoxytetramethylene,polyoxy-hexamethylene, ethylene oxide and propylene oxide block orrandom copolymers, and ethylene oxide and tetra-hydrofuran block orrandom copolymers. In particular, a polyoxyalkylene having from 2 to 4carbons in the alkylene moiety is preferred, with polyoxyethylene beingmost preferred. The number average molecular weight of thepolyoxyalkylene is from 200 to 6000, and preferably from 300 to 4000.

In the present invention, as examples of the ‘polymer (A) containingpolyether chains as structural units’ desirably used, there arepolyetherpolyamide block copolymers, polyetherpolyester block copolymersand polyetherurethanes. Of these, the polyetherpolyamide blockcopolymers are especially preferred.

The ‘polyetherpolyamide block copolymer’ used in the present inventionis a block copolymer in which there are linked together polyoxyalkylenechains (a) and polyamide chains (b) which comprise polymer of anaminocarboxylic acid or lactam having at least six carbons, or polymerof the salt of dicarboxylic acid and diamine with at least six carbons.Where (a) and (b) are alternately linked together via a dicarboxylicacid having from 4 to 20 carbons, the copolymers are generally referredto as polyetheresteramides, and these are also included in theinvention. Here, as the ‘aminocarboxylic acid or lactam having at leastsix carbons, or polymer of the salt of a dicarboxylic acid and diaminewith at least six carbons’, there are preferably used 11-aminoundecanoicacid, 12-aminododecanoic acid, caprolactam, laurolactam,hexamethylenediamine/adipic acid salt, hexamethylenediamine/sebacic acidsalt or the like. Further, in regard to aforesaid components (a) and(b), two or more types may also be jointly used together.

Such polymer is produced, for example, by the method described inJapanese Examined Patent Publication No. 56-45419. The types and amountsof the polyether and polyamide components in the block copolymer used inthe present invention are selected according to the objectives andapplication. From the point of view of water vapour permeability, waterresistance and the handling characteristics, etc, thepolyether/polyamide ratio is preferably from 4/1 to 1/4.

The ‘polyetherpolyester block copolymer’ employed in the presentinvention is one in which there are linked together polyoxyalkylenechains (a) and polyester chains (d) comprising polymer of ahydroxycarboxylic acid with at least six carbons or of a dihydroxycompound with at least two carbons and an aromatic dicarboxylic acid.Again, in regard to these (a) and (d) components, two or more types maybe jointly employed. Such polymer is produced for example by the methoddescribed in U.S. Pat. No. 4,739,012. The weight ratio of the aforesaid(a) and (d) components in the block copolymer employed in the presentinvention is determined by the objectives and the application. Eventhough they are similar thermoplastic elastomers, there is little effectwith polyester-polyester block copolymers. The ‘polyetherurethane’employed in the present invention is a thermoplastic polyurethaneemploying polyether as the soft segments, but there is little effectwith the polyester type or caprolactam type even though they are alsopolyurethanes. Specifically, the polyurethanes are normally obtained bythe reaction of an organic diisocyanate and a polyether of molecularweight from 500 to 6000 and, in some cases, chain extension is carriedout in the presence of catalyst. As the diisocyanate, there ispreferably employed tolylene diisocyanate, diphenylmethane diisocyanateor the like, and as the polyether there is preferably usedpolytetramethylene glycol or polypropylene glycol, etc.

These polyetherpolyamide block copolymers, polyether-polyester blockcopolymers and polyetherurethanes can be used singly or as mixtures, orthere can be used mixtures of two or more block copolymers havingdifferent types or a different ratio of the resins which respectivelyconstitute the soft and hard segments. Again, within a range such thatthe objectives of the present invention are realised, they may also beblends with other resins. From amongst these, the polyetherpolyamideblock copolymers are especially preferred.

In the present invention, ‘polyolefin (B)’ means a polymer containing anolefin component, for example a component such as ethylene, propylene orbutene-1, and the following can be cited as examples.

1) Polyethylene, polypropylene and copolymers of ethylene and α-olefins,and to these polymers there may also be grafted unsaturated carboxylicacid anhydrides such as maleic anhydride or unsaturated epoxides such asglycidyl methacrylate.

2) Copolymers of ethylene and at least one type of compound selectedfrom the group comprising (i) unsaturated carboxylic acids and the saltsand esters thereof, (ii) saturated carboxylic acid vinyl esters, (iii)unsaturated dicarboxylic acids and the salts, esters, hemi-esters andanhydrides thereof, and (iv) unsaturated epoxides, and to these ethylenecopolymers there may also be grafted unsaturated dicarboxylic anhydridesor unsaturated epoxides.

3) Optionally maleic-modified styrene/ethylene/butene/styrene (SEBS)block copolymer.

It is also possible to use a mixture of two or more types of sucholefins.

The ‘vinyl compound’ from which the ‘copolymer (C) of a vinyl compoundand an unsaturated dicarboxylic acid or derivative thereof’ is composedin the present invention is an α-olefin with from 2 to 8 carbons such asethylene, propylene, butene, isobutylene, isoamylene and n-hexene,preferably an α-olefin with from 4 to 6 carbons, or an aromatic vinylcompound or derivative thereof such as styrene, α-methylstyrene,vinyltoluene, t-butylstyrene and chlorostyrene. Further, the‘unsaturated di-carboxylic acid or derivative thereof’ from which (C) iscomposed is maleic acid, fumaric acid or the like, or the anhydride,ester, hemi-ester or salt thereof. These are polymerized under normalradical polymerization conditions.

Of these, copolymer comprising styrene or derivative thereof, and maleicacid or anhydride or ester thereof, is preferred. In such circumstances,the molar ratio of the styrene or derivative thereof to the maleic acidor derivative thereof is desirably from 1:1 to 4:1, and more preferablyfrom 2:1 to 4:1.

The ‘compatibilizing agent (D)’ used in the present invention is apolymer for enhancing the miscibility of the polymer (A) containingpolyether chains as structural units and the polyolefin (B), and it isat least one member of the group comprising ‘polyolefins or copolymersthereof with (meth)acrylate or vinyl acetate, which are grafted orcopolymerized with unsaturated carboxylic acid, unsaturated carboxylicacid anhydride or un-saturated epoxide’. Specifically, there can becited, maleic-anhydride-grafted polyethylene or polypropylene,ethylene/maleic anhydride copolymer, ethylene/alkyl acrylate or vinylacetate/maleic anhydride terpolymer and ethylene/alkyl acrylate/glycidylmethacrylate terpolymer, etc.

The blending proportions by weight of the polymer (A) containingpolyether chains as structural units, the copolymer (C) of a vinylcompound and unsaturated dicarboxylic acid or derivative thereof, and/orcompatibilizing agent (D), is A/C/D=50 to 95/0 to 20/0 to 40, andpreferably 50 to 90/0.1 to 10/1 to 30. (However, A+C+D=100)

Polyolefin (B) is blended after first melt blending the A, C and/or Dcomponents. If the B component is blended at the same time, the stablemoulding properties and uniform performance which are the objectives ofthe present invention are not obtained. Again, the blending proportionof the B component will differ with the desired performance, and isselected within the range A/B=1/99 to 99/1 according to the particularapplication. When used for the storage of items undergoing markedrespiration, it is recommended that A/B=99 to 55/1 to 45, and preferably95 to 60/5 to 40, while in the storage of items which are comparativelyreadily dried it is recommended that A/B=45 to 1/55 to 99, andpreferably 40 to 5/60 to 95. In such circumstances, the extrusionstability is also somewhat dependent on the melt viscosity, and in theformer case it is desirable that the viscosity of the A component below, while in the latter case that that of the B component be low. B theblending of these components in such proportions, it is possible toobtain stably and with good reproducibility moulded articles in whichthe moisture vapour permeability is controlled over a broad range whilestill maintaining a high gas permeability.

To give an example of the blending method of this resin composition,resins A, C and/or D are each optionally dried, after which they aredirectly melt extruded in the prescribed proportions, or they are meltextruded from a previously-prepared dry blend, and formed into pellets(master pellets). After this, these master pellets are dried whererequired and proportionally supplied or mixed with polyolefin (B) in theprescribed proportions and melt extruded, and then, with or withoutfirst pelletizing, the composition is passed through a T-die orblown-film die and film produced. For the molten mixing, there is usedan ordinary single-screw or twin-screw extruder, etc, and while themelting temperature will depend on the types of resins and theirblending proportions, in general from 120 to 250° C. is employed.

In the resin composition of the present invention there can be freelyincluded, within a range such that the characteristics of the inventionare not impaired, conventionally-known antioxidants, thermaldecomposition preventives, ultraviolet absorbers, hydrolysis resistanceimprovers, colouring agents (dyes, pigments), antistatic agents,electroconductive agents, crystallization nucleating agents,crystallization promoters, plasticiers, ready-slip agents, lubricants,release agents, flame retardants, flame retardant assistants and thelike.

The resin composition of the present invention can be used to produceextrusion moulded articles such as sheet, film and tube, etc, orinjection moulded articles such as containers, etc, and it can also beemployed by blending with other thermoplastic resins. When producingextrusion moulded articles, various kinds of methods can be used such asthe T-die system, etc, as well as blown film extrusion.

EXAMPLES

Below, the present invention is explained in more specific terms bymeans of some examples but it goes without saying that the presentinvention is not to be restricted solely to these. Now, in the examples,the values of the various properties were measured by the followingmethods.

(1) MFI (units: g/10 min)

Measured at 190° C., under a 2.16 kg load, based on ASTM D1238.

(2) Moisture permeability (water vapour permeability) (units: g/m².day)

The film was measured under conditions B (40° C., 90% relative humidity)based on JIS Z0208.

(3) Gas permeability (units: Ml/M².day.atm or %)

This was measured by the differential pressure method. The specificconditions were as follows.

Device: gas permeation measurement instrument model GTR-10XE made byYanako Binseki Kogyo (K.K.).

Test area: 15.2 cm² (44 mm diameter)

Test method: calibration curve system, based on a gas chromatograph withan attached TCD

Temperature, relative humidity: 25° C., 0% PH

Carrier gas: helium, 70 Kpa

Diffusion gas: CO₂/O₂/N₂/C₂H₄ (30.0/30.0/39.12/0.88 vol %)

(4) Transparency (units: %)

The haze was measured based on ASTM D1003

(5) Antistaticity (units: ohm/sq)

Surface resistivity was measured based on ASTM D 257.

Further, the resins employed were as follows.

A-1: polyetheresterpolyamide a block copolymer comprising polyoxyethyenechains and polyamide 12 chains (weight ratio 40/60)

A-2: polyetheresterpolyamide block copolymer comprising polyoxyethyenechains and polyamide 12 chains (weight ratio 50/50)

B-1: polyethylene of MFI 2, in which there is copolymerized 9 wt %methyl acrylate

B-2: polyethylene of MFI 1.6 and density 0.895 obtained bypolymerization using a metallocene catalyst

C-1: copolymer comprising styrene/maleic acid partial ester (molar ratio2/1) [acid value 220]

C-2: styrene/maleic anhydride (molar ratio 3/1) copolymer

D-1: ethylene/acrylate/maleic anhydride terpolymer containing 6 wt %comonomer and 3 wt % maleic anhydride

D-2: ethylene/glycidyl methacrylate copolymer containing 8 wt % glycidylmethacrylate

Example 1, Comparative Example 1

Resins A-1, C-1 and D-1 were mixed together in the proportions, byweight, of A/C/D=80/2.4/17.6, then melt extrusion carried out with atwin-screw extruder set at 160-180° C., followed by pelletizing, andmaster pellets obtained (taken as M1). These pellets were dried at 80°C. and then, along with resin B-1, proportional feeding was conducted ata weight ratio of 80/20 (M1/B1) using a single screw extruder fittedwith a T-die set at 180° C. at the tip, and film of thickness 25μobtained. The extrusion pressure was 8.5 MPa and the screw torque wasstable at 35 Nm. The variation in thickness of the film obtained in theextrusion direction and in the direction at right angles thereto was±0.1μ (this was taken as Film 1; Example 1).

Moreover, A-1, B-1, C-1 and D-1 were also directly dry blended in thesame proportions as above, namely A/B/C/D=64/20/1.92/14.08 by weight,and film of thickness 25μ produced using the same single screw extruderfitted with a T-die. The average extrusion pressure was 8.0 MPa and theaverage screw torque was 33 Nm, but both fluctuated considerably, andthe variation in film thickness was five times greater, at ±0.5μ (thiswas taken as Film 1′; Comparative Example 1).

The moisture permeability of Film 1 was 1200 g/m².day and the haze was8% and the surface resistivity was 5×10 E(11) ohm/sq, which were not atall inferior to the values for Film 1′ (1250 g/m².day and 7% and 9×10E(11) ohm/sq, respectively).

Example 2, Comparative Examples 2 and 3

The master pellets (M1) prepared in Example 1 were dry blended with B-2in proportions by weight of 40/60 and then, by using a single screwextruder fitted with a blown film die of diameter 15 cm and slit width0.6 mm, there was produced blown film of thickness 30μ at a blow-upratio of 1.5 (Film 2). The thickness variation was ±0.5μ, the moisturepermeability was 118 g/m².day and the haze was 11% (Example 2).

For comparison, the four resins were dry blended in the same proportions(A-1/B-2/C-1/D-1=32/60/0.96/7.04) and, using the same equipment, blownfilm was produced of thickness about 30μ. The moisture permeability was120 g/m².day and again the haze was about the same at 10%, but whencompared to Film 2 based on the master batch method the thicknessvariation was double, at ±1μ (Comparative Example 2).

Further, when blown film was produced in exactly the same way as inComparative Example 2 except that the C-1 component in that example wasnot used, the extruded film was unstable and, at times, the film came incontact with the cool ring where it emerged from the die, so that onlyfilm having an extremely poor surface state was obtained (ComparativeExample 3).

Examples 3 and 4

Master pellets (M2 and M3) comprising the proportionsA-2/C-2/D-1=75/20/5 and A-1/C-1/D-2=80/18/2 were prepared in the sameway as in Example 1. By the proportional feeding of these at a ratio ofM2/B-1=85/15 and M3/B-2=30/70 respectively, and using the same equipmentas in Example 2, blown film was produced. The film production processwas stable and it was possible to obtain a uniform film over a longperiod (Films 3 and 4).

Examples 5 and 6, Comparative Example 4

Film 1 and Film 4 were each cut to A4 size and by superimposing twosheets of each and heat-sealing three of the edges bags were produced(Bags 1 and 4). In Bag 1 there was introduced a peach (243 g), then thefinal edge heat-sealed and the bag stored at room temperature (average23° C.). After 1 week, the gas concentrations within the bag were 7%carbon dioxide and 7% oxygen. When the peach was inspected after openingthe bag, it was still fresh and the taste was good (Example 5).

When, for comparison, a peach was packaged in the same way using acommercial 25μ low density polyethylene bag and heat-sealed, and thenstored for 1 week at room temperature, there was a smell of alcohol fromthe peach and mould had developed (Comparative Example 4).

Further, three Valencia oranges were placed in Bag 4, the remaining edgethen heat-sealed and the bag stored for 3 months at room temperature.Even after 3 months the appearance and taste of the oranges were good(Example 6).

EFFECTS OF THE INVENTION

As explained above, in the present invention a reactive compound isblended in prescribed proportions with a polymer having polyetherchains, and then in stepwise fashion, blending and dilution by means ofpolyolefin, and moulding are conducted and, in this way, it is possibleto obtain with good reproducibility, uniform moulded articles havingdesired water vapour permeability over a broad range while stillmaintaining a high gas permeability. In particular, it is possible toobtain films having a low variation in thickness as shown by thepreceding examples.

What is claimed is:
 1. A method of manufacturing a thermoplasticcomposition comprising: melt blending (A) a polyetherpolyamide blockcopolymer with (C) a copolymer of styrene and either maleic anhydride ormaleic acid wherein the molar ratio of styrene to maleic acid or maleicanhydride lies in the range from 1/1 to 4/1, and optionally (D) at leastone grafted or copolymerized comparibilizer selected from the groupconsisting of (a) a polyolefin, (b) a copolymer of an olefin with(meth)acrylate and (c) a copolymer an olefin with vinyl acetate, said(a), (b) and (c) being grafted or copolymerized with at least one of anunsaturated carboxylic acid, an unsaturated carboxylic acid anhydrideand an unsaturated epoxide, to produce a melt blended mixture;pelletizing the melt blended mixture; and then blending (B) a polyolefinwith the resultant pelletized mixture.
 2. A method of manufacturing athermoplastic resin composition according to claim 1, which ischaracterized in that in the composition comprising (A) plus (C) andoptionally (D) prior to the blending of the polyolefin (B), the blendingproportions by weight of (A)/(C)/(D) are 50 to 95/more than0 to 20/0 to40, wherein A+C+D=100.
 3. A method of manufacturing a thermoplasticresin composition according to claim 2, comprising melt-blending thecompatibilizing agent (D).
 4. A method according to claim 3, furthercomprising extruding the resultant blend containing the polyolefin toproduce a film.
 5. A film produced according to claim
 4. 6. A methodaccording to claim 1, wherein the resultant melt-blended mixturecontains (A), (C) and (D).
 7. A method according to claim 6, furthercomprising extruding the resultant blend containing the polyolefin toproduce a film.
 8. A film produced according to claim
 7. 9. A filmaccording to claim 8, having relative proportions of (A), (C) and (D) toone another of about 75-80/20-18/5-2 respectively.
 10. A film accordingto claim 9, wherein (D) is either ethylene/acrylate/maleic anhydrideterpolymer or ethylene/glycidyl methacrylate.
 11. A method according toclaim 1, further comprising extruding the resultant blend containing thepolyolefin to produce a film.
 12. A film produced according to claim 11.